The odd pairing of the elder Hollywood crooner and the younger glam-rock god was put together for what would turn out to be Bing Crosby's last television Christmas special, which merged the very familiar holiday song, "The Little Drummer Boy" with an original song written for the show, "Peace on Earth". This was done, apparently, because David Bowie hated the drummer boy song and didn't want to sing it. That turned out to be a blessing in disguise because it gave the song a fresh take and a Christmas classic was born.
"The Little Drummer Boy/Peace On Earth" - Bing Crosby & David Bowie (1977)
Here is the clip from the TV special: